Decibels, translated.
Noise is the spec owners complain about most — and the hardest to shop for, because decibels don't mean anything until you've lived with them. Here's the scale, the traps, and the numbers to hold a purifier to.
The decibel scale, in plain terms
Decibels are logarithmic: every +10 dB sounds roughly twice as loud. A purifier at 50 dB isn't a bit louder than one at 40 — it's double. Small differences in the spec sheet are big differences in your bedroom.
| Level | Sounds like | Verdict |
|---|---|---|
| 20 dB | A whisper, rustling leaves | Inaudible for most sleepers |
| 30 dB | A quiet library | The bedroom ceiling — under this is the goal |
| 40 dB | A refrigerator hum | Fine for living rooms, distracting at night |
| 50 dB | Moderate rainfall | Daytime only |
| 60 dB | Normal conversation | You'll hear it across the room |
Read both numbers: min and max
Manufacturers advertise the minimum — the sleep-mode whisper. But CADR is measured at the maximum, where many purifiers hit 55–65 dB: conversation volume. A unit that's silent on low but jet-engine loud on high will live on low, where its effective CADR is a fraction of the advertised number.
The fix is headroom: buy enough CADR that a quiet middle setting still delivers your two-thirds target. For bedrooms, hold the line at under 30 dB on the lowest setting — and check for a display-off mode and no button beeps while you're at it.
Quietest settings across 68 tracked models
Where the index lands on minimum noise. Most modern purifiers clear the 30 dB bedroom bar on their lowest setting — the spread is in how much air they move while doing it.
What owners say about noise.
Fan hum, rattles, and 2 a.m. auto-mode surges — real complaints and praise from Reddit threads.